A 5 mm crochet hook is a US H-8, and the millimetre size is the one to trust. Use the converter above to turn millimetres into a US size, or a US size into millimetres, and to see which yarn weights suit that hook. The Craft Yarn Council chart below gives 25 sizes, from 2.25 mm (US B-1) to 30 mm (US T/X), so you can compare your hook with the rest of the range.
How do you use the hook size converter?
Pick regular or steel, then type a size in millimetres or choose a US letter or number. The match appears at once. Under it, the tool lists every yarn weight whose recommended hook range includes your hook, from the finest weight, 0 Lace, up to the thickest, 7 Jumbo, and that list is the quickest way to see what yarn the hook was made to work with.
Start from the millimetre size whenever you can, because it is the diameter of the hook and reads the same on every brand. A US letter is only a label. If your hook has no size stamped on it, measure the shaft and look that number up.
How do you read the converter result?
A US label can point to more than one millimetre size. On this chart, US Q is both 15.75 mm and 16 mm. The Craft Yarn Council adopted metric sizing because companies numbered their US hooks in different ways, so the council calls the millimetre size the more accurate one. When a label matches several sizes, the converter says so. Use the millimetres.
The yarn weights listed under the result are a guide, not a rule. A 5.5 mm (US I-9) hook sits in the range for weight 3 Light and for weight 4 Medium, so both appear. Pick the one that matches your yarn label, and read the label twice. The council states its ranges are guidelines only, so a hook named in your pattern beats anything on this page.
What is the crochet hook size chart?
The chart gives 25 regular hook sizes in millimetres, each with the US size the Craft Yarn Council gives for it.
| Millimetres | US size |
|---|---|
| 2.25 | B-1 |
| 2.75 | C-2 |
| 3.125 | D |
| 3.25 | D-3 |
| 3.5 | E-4 |
| 3.75 | F-5 |
| 4 | G-6 |
| 4.25 | G |
| 4.5 | 7 |
| 5 | H-8 |
| 5.25 | I |
| 5.5 | I-9 |
| 5.75 | J |
| 6 | J-10 |
| 6.5 | K-10 1/2 |
| 8 | L-11 |
| 9 | M/N-13 |
| 10 | N/P-15 |
| 11.5 | P-16 |
| 15 | P/Q |
| 15.75 | Q |
| 16 | Q |
| 19 | S |
| 25 | T/U/X |
| 30 | T/X |
Which hook size suits which yarn weight?
Each yarn weight has a recommended hook range, and the ranges meet at their edges, so a hook at the boundary appears under two weights because both ranges include it. For worsted, afghan or aran yarn, weight 4 Medium, the range is 5.5 to 6.5 mm (US I-9 to K-10 1/2).
| Yarn weight | Name | Recommended hook |
|---|---|---|
| 0 | Lace | 2.25 mm |
| 1 | Super Fine | 2.25 to 3.5 mm |
| 2 | Fine | 3.5 to 4.5 mm |
| 3 | Light | 4.5 to 5.5 mm |
| 4 | Medium | 5.5 to 6.5 mm |
| 5 | Bulky | 6.5 to 9 mm |
| 6 | Super Bulky | 9 to 15 mm |
| 7 | Jumbo | 15 mm and larger |
The full list of yarn types for each weight is on the yarn weight chart.
What hook size mistakes should you avoid?
Hook trouble usually comes from three habits.
- Trusting the letter alone. Two hooks with the same US letter can differ in width. Check the millimetres on the shaft.
- Mixing up steel hooks. Steel hooks are numbered in reverse, so a higher number means a smaller hook. The council’s lace weight row lists steel hooks of 1.4 to 1.6 mm, covering US steel sizes 6, 7 and 8.
- Skipping the swatch. The council says to work a gauge swatch whatever the number or millimetre size, and to compare it with your pattern. A hook that matches the yarn label can still give the wrong fabric for your hands.
New to the craft? The guide to how to single crochet names a hook range for worsted yarn and walks through the first stitch. For a hat, the hat size chart turns your gauge into a stitch count.
Questions makers ask
What hook is US G or US I?
On the Craft Yarn Council chart, US G is 4.25 mm and US I is 5.25 mm. Nearby labels sit close together: G-6 is 4 mm and I-9 is 5.5 mm. Read the millimetres on the shaft to tell them apart, and trust that number over the letter.
What if my hook sits on the edge of two yarn weights?
A hook such as 5.5 mm (US I-9) appears under weight 3 Light and weight 4 Medium, because both ranges include it. The council calls its ranges guidelines only, so work a gauge swatch with your yarn and compare it with your pattern before you commit.
Why are 2.5, 7 and 12 mm missing from the chart?
This page gives 25 sizes and states no US size for 2.5, 7 and 12 mm. If your hook is one of those, go by the millimetres, which the Craft Yarn Council calls the more accurate measurement, and confirm the fit with a gauge swatch.
How do steel crochet hook numbers work?
The council numbers steel hooks in reverse, so a higher number means a smaller hook. Its lace weight row lists steel hooks of 1.4 to 1.6 mm, covering US steel sizes 6, 7 and 8. It also publishes a separate steel hook and thread chart from 0.60 mm to 3.50 mm.
